using unique_ptr in constructor

Question

I am working on a school project and I cannot figure out unique_ptr usage.

class ClassName
{
private: 
    unique_ptr <bool[]> uniquePtr;

    void func(unique_ptr<bool[]>& refPtr) const
        {
            refPtr[0] = true;
            refPtr[1] = false; 
        }
public:
    //other things that will use the array uniquePtr
};

ClassName::ClassName()
{
    bool* boolName = new bool [someSize()];
    uniquePtr = unique_ptr<bool[]>(boolName);
    func(uniquePtr);
    for(int i =0; i<someSize(); i++)
        {
            cout << uniquePtr[i];
            //This is all O's
        }
}

This does not work because uniquePtr is set to all 0s as func() finishes. I cannot figure out how to modify uniquePtr such that it will be accessible to my other functions. I do not have tried creating a new unique_ptr to pass into func() and then use move(uniquePtr) but that won't even compile.

If the uniquePtr is modified by a function, in this case assigning it boolean 1 or 0, shouldnt it be accessible to function outside of that in the class? If I print uniquePtr[index] within the function it gives me the expected results.

Thanks for the help!

Answer 1

A unique_ptr is not destroyed by passing it to a function by reference, so you are safe here.

However, passing unique_ptr by reference may not be the best way to express the idea. A non-owning pointer is represented by a plain C-style pointer in C++, so it's safe and idiomatic to do this:

void func(bool (*ptr)[]) const { ...

and then

func(uniquePtr.get());

As mentioned in the comments, data members should be initialised like this:

ClassName::ClassName() : unique_ptr(new bool[someSize()]) {
    func(uniquePtr.get());
}

(use std::make_unique instead of new if you can)